Pros Need to Pay Close Attention to the Standards and Rules of Rigging.
Picture this: An enthusiastic, enterprising fellow decides to hang six large loudspeakers in a warehouse for a weekend party. The overhead beams look strong and secure, and while there's no mounting hardware, the handles on the enclosures look sturdy enough. What could possibly go wrong? OK, before you say, “It could never happen” — yes, it could happen, and it does happen periodically. The lucky ones are those not maimed or killed when speakers come crashing down at 3 a.m.
Fortunately, in contrast to a decade ago, pros handling loudspeaker rentals have become more educated about risks involved, not only to their clients, but also to their company's business. Even so, there are a lot of fly-capable loudspeakers sold or rented into markets where no one thinks of consulting a structural engineer or hiring a rigger. So while the designs of loudspeaker enclosures and rigging hardware have become fairly idiot-proof, you never know what someone will try.
In this column, I'll cover some of the basic issues surrounding rigging hardware and loudspeaker enclosure. For some guidance, I spoke with a number of people, including Andrew Martin, CEO of ATM Flyware of Carson, Calif., a company specializing in the design and manufacturer of rigging hardware. I also had a chance to get perspectives from Mark Engebretson, director of systems development at JBL Professional in Northridge, Calif., and John Monitto, technical manager at Meyer Sound in Berkeley, Calif.
Safe rigging begins with having flyable enclosures, or enclosures that have been certified that they're both capable of being hung and have been tested for load limitations. Many loudspeaker manufacturers build enclosures that aren't flyable, however. For these, internal brace kits (available through companies like ATM Flyware) can be installed in the enclosure so it can safely handle the increased load once it's flown. In the end, the enclosure should be able to handle five times the loads applied to it.
Currently, there are no observed standards for the construction and testing of loudspeaker enclosures. Through the theatrical organization ESTA, however, there is a Loudspeaker Rigging Standards group that has proposed such a standard (BSRE1.8). This proposed standard was in its final revision and review phase at press time. Chaired by Andrew Martin and including the participation of several key loudspeaker manufacturers, the group proposes a 5:1 design factor for predictable components — that is, components made out of metal, aluminum, or a carbon with predictable structural characteristics. In that case, you could safely count on a 5:1 design factor to more than accommodate for misuse of the product.
By contrast, Martin says the Uniform Building Code ranges in design factor from 1.4:1 to 1.7:1. “So here, we are doing a 5:1 design factor as an entertainment industry, mutually-agreed-to factor,” says Martin. “And it works fairly well because we don't have too many accidents.”
The proposal also offers a 10:1 standard for materials that are not predictable. These include plywood, fiberglass, and rotational molded boxes, the latter being very unpredictable due to varying thickness at any given point. This doesn't mean that a loudspeaker enclosure has to have a 10:1 factor. It means that if the hardware component — for example, a track system — fails first in testing, then you can put a 5:1 design factor since the enclosure is stronger than the hardware. However, if the enclosure fails first, then it's 10:1. Confusing initially, but sensible when you think about it.
There are different load rating methods used in the industry — the two most common being the result of the ultimate strength load of a component or a result of the yield strength load of the component. Rigging hardware manufacturers will use either method, so whoever is rigging the enclosure should know which one was used since there are limitations to each one.
Joining and Bracing the Box
There are various joinery methods used in an enclosure, but the way they test and fail can be quite different. The most common method is dado-type construction, which is easy to manufacture, fast, and self-aligning. It's therefore no surprise that most manufacturers use this approach. Not the weakest nor strongest method, dado is a good middle ground and quite predictable. The strongest way to build an enclosure is with a rabbet and dado construction, but it's next to impossible to deal with on a production basis — very expensive in terms of labor cost — so this approach is used mostly by people building proprietary boxes.
Different types of bracing methods are used to reinforce the joint of the enclosure. While there are external bracing systems, internal bracing is more common. In practice, the internal brace mounted around edges of the enclosure can help distribute force from the top and bottom of the enclosure to the sides.
One of the stronger methods of bracing, however, is through-enclosure bracing. Here, a threaded rod or flat strap joins top and bottom braces. While the drawback can be compromised acoustic characteristic of an enclosure, it can be ideal for line arrays, where most of the torsion in the system is absorbed by the enclosure, not the rigging hardware. This was an unforeseen challenge that required strengthening the enclosure.
“There was a time when line arrays got thin with wood and lightweight construction, and the boxes would crack,” says Martin. “Nothing would fall but they would crack.”
In time, several manufacturers began to design the rigging system in conjunction with the line arrays because you can come out with an end product that's a lot lighter, but still distributes the stress with no problems.
“Most line arrays that you'll see on the market today are boxes with rigging thrown on them,” adds Martin. “In the coming year or two, you'll see more boxes with the rigging system included. And you'll see a big difference.”
Two companies that have made the move toward designing all aspects of their line arrays in-house are Meyer Sound and JBL. At Meyer, John Monitto suggests there really was no other option.
“It had to come in-house because it was a more important part of how the system was put together and how fast it flew out,” says Monitto. “We had to look at it fresh and design rigging into the cabinet. And all the competition is doing that now.”
Like most companies, Meyer Sound believes that part of selling a system now involves educating people on not only how to best put it in and optimize the acoustics, but also focus on rigging issues. Recent additions to their MAPP online modeling software include a structural calculator allowing users to determine the weight on the front and back motor with various line array systems.
JBL's Mark Engebretson says that both the Vertec and HLA lines likewise had all rigging design done in-house. “We wanted to exert a little more control over our designs, and in the case of Vertec, it was inexorably linked to making it work,” says Engebretson. “The tolerance stack up included both the cabinets and the rigging hardware, as well. We didn't see any other reasonable way to go about this.”
JBL also includes a line array calculator on its rigging pages online to help users determine the center of gravity and what the loading is on each suspension point.
“Very few people realize that, from a manufacturer's perspective, when we build hardware, we have to watch out for two things,” says Martin. “We have to mitigate our own risk as a manufacturer, and we want to mitigate the risk of the people that use our hardware.”
Martin believes the way to do that is to run control systems around the hardware, around the design, and around the fabrication of the hardware. He calls this “product traceability,” where anything used for overhead suspension has to be traceable. “This would mean that a broken part tells you where the materials came from, who made it, and who did the quality checks. If the part was bad, you can find out which batch those parts went from to arrange for a recall,” he explains. “Also, if you're doing a high-risk component, whether it's a loudspeaker or rigging, you need to put in specific instructions on how it's to be used, and how it's to be inspected and maintained.”
These are two methods a manufacturer might use to mitigate its own risk. But service companies, contractors, and rental companies better look to mitigate their risk, as well, no matter who made the equipment.
“If there's an accident, it can put your company out of business,” Martin warns.
Alex Artaud is a writer, musician and engineer living in Oakland, Calif.
Email him at firstname.lastname@example.org.